Thaw half of the frozen blueberries (⅔ cup) in the microwave. This should only take 30 seconds or so. Set aside.
Preheat the oven to 350ºF and prepare two large cookie sheets with parchment paper.
In the bowl of a stand mixer with the flat beater attachment or a large mixing bowl with an electric mixer, combine the sugar and lemon zest and mix on high for 1 minute.
Add in the butter and thawed blueberries and cream together until light and fluffy. This should take approximately 2 minutes.
Pour in the lemon juice and mix until fully combined.
Add the flour, cornstarch, baking powder, and salt and mix on low until a dough forms. Scrape down the sides of the bowl with a spatula when needed.
With a spatula, combine the remaining frozen blueberries (⅔ cup), into the dough until just combined.
Using a 1.5 tablespoon cookie scoop, scoop the cookie dough onto the prepared cookie sheets approximately 2 inches apart and bake for 13-15 minutes or until the edges are set and the center appears slightly underbaked.
Remove from the oven and allow the cookies to cool for 10 minutes on the tray before removing to a rack to fully cool. Enjoy!
Store leftover cookies in an airtight container at room temperature for up to 5 days and frozen for up to 6 months.
